Scratch is a treat, so a small amount occasionally is plenty. It helps to train them to come when called! Cold weather is irrelevant; the whole 'corn for heat' thing is fantasy. Good food, free choice, and blocking wind and wetness, are what they need.
I give a heaping 1/4 cup measure to three 31 month olds as a midmorning treat.
I give the same 1/4 measure to seven 12 week olds.
A fresh complete feed fed free choice and fresh water is best to keep chickens healthy and warm. GC